An instrument of this type is described in my U.S. Pat. No. 3,651,780; it has a fixed pointer or mark and a rotatable cylindrical scale which is read against the mark. The instrument of U.S. Pat. No. 3,651,780 includes an epicyclic gear system drive which although efficient and effective is relatively expensive to manufacture.
An object of the present invention is to provide an instrument which is simpler and hence cheaper to manufacture than the instrument of U.S. Pat. No. 3,651,780.
A further object is to provide such a simpler instrument in which the drive ratio can be 1.27:1 instead of 2.54:1 so that when the instrument is adapted for use with an English leadscrew, the increase in the speed of rotation of the scale when set for Metric representation is more acceptable to the eye. Also the rate of wear is reduced.
Yet a further object of the invention is to provide an instrument which is simple to adapt for use with either English or Metric leadscrews.
Yet a further object of the invention is to provide an instrument in which the setting of a zero reading is readily and positively accomplished.